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blist_meta_alloc assumes that mask=scan->bm_bitmap is nonzero. But if the

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cursor lies in the middle of the space that the meta node represents, then
blanking the low bits of mask may make it zero, and break later code that
expects a nonzero value.  Add a test that returns failure if the mask has
been cleared.

Submitted by:	Doug Moore <dougm@rice.edu>
Reported by:	pho
Tested by:	pho
X-MFC with:	r340402
Differential Revision:	https://reviews.freebsd.org/D18058
This commit is contained in:
Alan Cox 2018-11-24 21:52:10 +00:00
parent 80203ccefd
commit ee73fef96e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=340914
1 changed files with 2 additions and 0 deletions
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sys/kern/subr_blist.c
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@ -764,6 +764,8 @@ blst_meta_alloc(blmeta_t *scan, daddr_t cursor, daddr_t count, u_daddr_t radix)
/* Discard any candidates that appear before cursor. */
digit = (cursor / radix) & BLIST_META_MASK;
mask &= (u_daddr_t)-1 << digit;
if (mask == 0)
return (SWAPBLK_NONE);
/*
* If the first try is for a block that includes the cursor, pre-undo